The present invention relates to light emitting diodes with light filters and methods of manufacturing thereof.
Solid state light emitting devices, such as inorganic or organic Light Emitting Diodes (LED or LEDs), convert energy to light and are widely used for many applications. As known to those having skill in the art, inorganic solid state devices generally include one or more active regions of semiconductor material sandwiched between oppositely doped regions. When a bias is applied across the doped regions, electron-hole recombination events occur to generate light and in turn, light is emitted from the active region in omnidirectional paths and from all surfaces of the LED. Conventional LEDs may incorporate reflectors and/or mirror surfaces to direct the emitted light in a desired direction.
The color or wavelength emitted by an LED is largely dependent on the materials from which it is formed and its resulting materials properties, such as the bandgap of the active region. These colors or wavelengths include red, yellow, green, and blue in the visible spectrum as well as the ultraviolet (UV) portions of the electromagnetic spectrum. It is often desirable to incorporate phosphor into a light emitting diode, to enhance the emitted light in a particular wavelength and/or to convert at least some of the light to another wavelength. As used herein, the term “phosphor” is used generically for any photoluminescent material. The phosphor may be located anywhere within the LED device and may be formed using many techniques.
For example, phosphor may be coated inside and/or outside a dome-shaped shell that covers the device and/or included within the shell itself. The phosphor may be located remotely from the light emitting die or it may be coated or deposited on the die itself. These techniques may include electrophorectic deposition, stencil printing, spin or spray coating, etc. Other techniques may include a phosphor dispense, where a drop of material, such as epoxy, silicone encapsulant, etc., that contains phosphor therein, may be placed on the die and cured to form a shell over the die. This technique may be referred to as a “glob top”. In other techniques, the drop of material that contains phosphor may be placed on the die and the phosphor may be allowed to settle on the die. This technique may be referred to as “remote settling”.
It is often desirable to configure a light emitting device to emit white light. As used herein, the term “white light” is used in a general sense and includes light that different individuals or detectors may perceive as having a slight tint toward, for example, yellow or blue. Conventional LED devices may combine a yellow phosphor on a blue LED to achieve white light. Some of the blue light emitted from the LED passes through the phosphor without being converted and some of the emitted blue light is down-converted to yellow. The combinations of blue light and yellow light that escape the light emitting device provide visible white light output.